chore(Python): add graph (#495)

Co-authored-by: Ming Tsai <37890026+ming-tsai@users.noreply.github.com>

algorithms/Python/README.md

@@ -56,6 +56,13 @@
 - [Catalan Sequence](dynamic_programming/catalan_sequence.py)
 - [0/1 Knapsack Problem](dynamic_programming/knapsack.py)
 
+## Trees
+- [Binary Tree](trees/binary_tree.py)
+
+## Graphs
+- [Simple Graph](graphs/graph.py)
+
 ## Trees
 - [Binary Tree](trees/binary_tree.py)
 - [Binary Search Tree](trees/binary-search-tree.py)
+

algorithms/Python/graphs/graph.py

@@ -0,0 +1,139 @@
+# author: @hashfx
+
+# Graph Visualization
+
+#                 member1--member5
+#                    |
+#         member3--member0--member2
+#                    |
+#                  member4
+ 
+ 
+#             |------city1----city3
+#             |        |       |
+#          city4----city2------|
+#                            city5
+
+
+# Graph Usage
+#     Facebook Friends Suggestion
+#         [m0 is friend of m1 & m5 is friend of m1; it is likely that m0 is friend of m5 too...
+#             FB will suggest m5 as friend suggestion to m0]
+#     Flight Routes : To find shortest path between two nodes
+#         [(city1,city2),(city1,city3),(city1,city4),
+#          (city2,city1),(city2,city4),(city2,city5),
+#          (city3,city1),(city3,city5),
+#          (city4,city1),(city4,city2),
+#          (city5,city2),(city5,city3)]
+#     Google Maps
+#     Internet
+#     E-commerce shopping Recommendation
+
+# Difference between TREE and GRAPH:
+#     In TREE, there is only one path between two nodes. GRAPH is a complex DS where two nodes can randomly be connected
+
+
+class Graph:
+    def __init__(self, edges):
+        self.edges = edges
+        # Transform route tuple to route dictionary
+        self.graph_dict = {}  # blank dictionary
+        for start, end in self.edges:
+            if start in self.graph_dict:  # element1 is already in dictionary
+                self.graph_dict[start].append(end)  # add another element associated to element1 in graph_dictionary
+            else:
+                self.graph_dict[start] = [end]  # if element1 is not present, add it to graph_dictionary
+        print("Graph dictionary: ", self.graph_dict)  # print route dictionary
+
+    # get paths between start-point and end-point
+    def getpath(self, start, end, path=[]):
+        path = path + [start]
+        if start == end:
+            return [path]
+
+        if start not in self.graph_dict:  # if one-way between one node, say Chennai; return []
+            # Chennai is not as a starting point, so it has no route associated
+            return []
+
+        paths = []
+        for node in self.graph_dict[start]:
+            if node not in path:
+                new_path = self.getpath(node, end, path)
+                for p in new_path:
+                    paths.append(p)
+        return paths
+
+    # method to find shortest path between start-point and end-point
+    def getShortestPath(self, start, end, path=[]):
+        path = path + [start]
+
+        # if starting-point and end-point are same
+        if start == end:
+            return path
+
+        # If no path available from a point, return None
+        if start not in self.graph_dict:
+            return None
+
+        # searching for shortest path
+        shortest_path = None  # shortest path initialised
+        for node in self.graph_dict[start]:
+            if node not in path:
+                sp = self.getShortestPath(node, end, path)
+                if sp:
+                    # if no shortest path is available; but in later iteration, we may have a path
+                    # so check if it is shorter than original path (array of routes) or not
+                    if shortest_path is None or len(sp) < len(shortest_path):
+                        shortest_path = sp  # shortest path returned
+
+        return shortest_path
+
+
+
+
+if __name__ == '__main__':
+
+    routes = [
+        ("Mumbai","Pune"),
+        ("Mumbai", "Surat"),
+        ("Surat", "Bangaluru"),
+        ("Pune","Hyderabad"),
+        ("Pune","Mysuru"),
+        ("Hyderabad","Bangaluru"),
+        ("Hyderabad", "Chennai"),
+        ("Mysuru", "Bangaluru"),
+        ("Chennai", "Bangaluru")
+    ]
+
+    routes = [
+        ("Mumbai", "Paris"),
+        ("Mumbai", "Dubai"),
+        ("Paris", "Dubai"),
+        ("Paris", "New York"),
+        ("Dubai", "New York"),
+        ("New York", "Toronto"),
+    ]
+
+    route_graph = Graph(routes)
+
+    ''' start == end
+    start = "Mumbai"
+    end = "Mumbai"
+    [op]: [['Mumbai']]'''
+
+    ''' start not in self.graph_dict
+    start = "Chennai"
+    end = "Mumbai"
+    [op]: []'''
+
+    start = "Mumbai"
+    end = "New York"
+
+    print(f"All paths between: {start} and {end}: ",route_graph.getpath(start,end))
+    print(f"Shortest path between {start} and {end}: ", route_graph.getShortestPath(start,end))
+
+    start = "Dubai"
+    end = "New York"
+
+    print(f"All paths between: {start} and {end}: ",route_graph.getpath(start,end))
+    print(f"Shortest path between {start} and {end}: ", route_graph.getShortestPath(start,end))